The present invention relates generally to a manner by which to facilitate improved communication quality of a communication signal transmitted upon a communication link in a communication system, such as a cellular radio communication system. More particularly, the present invention relates to apparatus, and an associated method, by which to select a link parameter of a communication signal transmitted by a sending station upon the communication link. In one implementation, uplink sounding bursts are transmitted by a mobile station and utilized to determine the link parameters to be exhibited by subsequently-generated communication signals.
Communication through the use of wireless communication systems has achieved wide popularity in recent years. Multi-user, wireless communication systems of improved capabilities have been implemented as a result of advancements in communication technologies. Communication pursuant to such multi-user, wireless communication systems can be affordably made, further increasing the popularity of usage of such systems.
In a wireless communication system, a communication channel formed between a sending station and a receiving station is a radio channel defined upon a portion of the electromagnetic spectrum. Because a radio channel forms a communication link, a wireline connection is not required to be formed between the sending and receiving stations to permit the communication of information between the stations. Communication by way of a wireless communication system is thereby permitted at, and between, locations at which the formation of a wireline connection would not be practical. Also, because a communication channel is formed of a radio channel, a radio communication system can be more economically installed as the infrastructure costs associated with a wireline communication system are significantly reduced.
A cellular communication system is exemplary of a wireless, multi-user radio communication system which has been made possible due to advancements in communication technologies and which has achieved wide levels of usage. A cellular communication system efficiently utilizes the portion of the electromagnetic spectrum allocated thereto. A plurality of fixed-site base stations are installed throughout a geographical area. By transmitting relatively low-power signals, the same frequencies can be reused at different locations throughout the geographical area. Thereby, communications can be effectuated between more than one set of sending and receiving stations concurrently at separate locations throughout the area encompassed by the cellular communication system.
Cellular standards have been promulgated relating to various types of cellular communication systems, and various types of cellular communication systems have been constructed corresponding to such standards. Several of such standards pertaining to a cellular communication system utilize TDMA (time-division, multiple-access) communication techniques. In a TDMA communication system, a carrier is divided into time slots in which a carrierxe2x80x94time slot combination defines a channel. Groups of adjacently-positioned time slots sometimes are together defined to form a frame, and group of frames are sometimes together defined as superframes or hyperframes.
In a particular communication session, one or more time slots per frame is allocated to a sending-receiving station pair to effectuate the communication of data therebetween. Because a single frequency bandwidth can be utilized to effectuate more than one communication session, improved communication capacity of the communication system is possible.
In an ideal communication system, a communication signal, when received at a receiving station, is substantially identical to the corresponding communication signal when transmitted by a sending station but delayed in time. However, in a non ideal communication system in which the communication signal must be transmitted upon a non ideal communication channel, the signal, when received at the receiving station is dissimilar to the corresponding communication signal when sent by the sending station. Distortion of the communication signal caused by transmission of the communication signal upon the communication channel causes such dissimilarities to result. If the distortion is significant, the informational content of the signal cannot be recovered at the receiving station.
In the aforementioned, TDMA cellular communication system, the communication channel, formed of a radio link, might be of characteristics which distort the values of the data bits of which a communication signal is formed. Fading, such as that caused by multi-path transmission or Rayleigh fading, alters values of the data bits of the communication signal during its transmission. Such distortion, if not corrected, reduces the communication quality levels of communications in a communication session formed between a mobile station and another station. Problems are sometimes most problematical when a mobile station is positioned at a cell-edge during a communication session. An increased path length between the mobile station and a base station resulting from position of the mobile station increases the possibility of increased levels of multi-path distortion as well as reducing the power level of a signal, when received at a receiving station. Also, co-channel, and other, interference with communications in other cells is more likely to be significant when the mobile station is positioned at a cell-edge.
Various techniques are utilized to overcome distortion introduced upon a communication signal as a result of transmission upon a non ideal communication channel. Channel encoding of the communication signal, prior to its transmission, for instance, increases the redundancy of the transmitted signal. By increasing the redundancy, the likelihood that the informational content of the signal can be recovered, once received at the receiving station, is increased. Alteration of the modulation format by which a communication signal is formed is sometimes also utilized to increase the likelihood that the informational content of the transmitted signal can be recovered. In a communication system which utilizes feedback acknowledgments of transmitted signal portions, power control schemes utilizing power control step size increments or decrements are utilized to increase, or decrease, the power levels of a transmitted signal, dependent upon channel characteristics. Selection of the number of times in which a signal portion is retransmitted or a selection of a timing of retransmission of a signal portion in the absence of positive acknowledgments also are utilized in some communication systems to overcome problems associated with non ideal channel conditions.
In some communication systems, communication signals are transmitted in bursts. Communication of GPRS (general packet radio service) messages proposed for the GSM (global system for mobile communications) family of standards is exemplary of communications which are effectuated in discrete bursts. Because of the bursty nature of the GPRS communications, additional difficulties in selecting the link parameters to communicate the messages is made more difficult. That is to say, GPRS messages are transmitted at intermittent intervals. The channel characteristics at the successive intervals during which the GPRS signals are transmitted might well differ significantly from one another. As a result, link parameters most appropriate to facilitate a good quality level of communications during one burst might be inappropriate to maximize communication quality levels at a subsequent interval.
If a manner could be provided by which to facilitate the selection of link parameters to communicate communication signals at improved communication quality levels, improved communication system performance would result.
It is in light of this background information related to radio communications that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to select link parameters of a communication signal transmitted by a sending station upon a communication channel of a communication system. The link parameters are selected responsive to indications of channel characteristics of the communication channel upon which the communication signal is to be transmitted. The coding rate, modulation format, power control step size, retransmission limits, and timer value are all exemplary of link parameters selectable during operation of an embodiment of the present invention.
Dynamic selection of one or more link parameters is made during operation of the communication system. If a determination is made that the channel characteristics have changed, appropriate alteration of the one or more link parameters is made, thereby to facilitate communication of subsequently-generated communication signals at an optimal communication quality level.
In one aspect of the present invention, sounding bursts are generated by a mobile station operable in a cellular communication system. The sounding bursts are generated when the mobile station is in a standby state. The sounding bursts are, for instance, shortened versions of access bursts, conventionally utilized in existing GSM (global system for mobile communications) systems. The sounding bursts are transmitted by mobile stations operable in the communication system according to a schedule provided thereto, such as network-generated sounding schedules downloaded to the mobile station by way of the downlink channel. The sounding schedules are, for instance, associated with the ESN (electronic serial number) or other indicia which identifies the mobile station. Analysis of the sounding bursts, when detected at the network infrastructure of the communication system, permits the estimation of channel characteristics of the uplink channel. In a GSM system which provides for GPRS (general packet radio service) communications, the mobile station is instructed to transmit the sounding burst periodically in an assigned position of a GPRS multiframe defined in the communication system. And, by limiting the transmission of the uplink sounding bursts to occur only when the mobile station is in a radio resource (RR) standby state, the number of sounding bursts generated by a mobile station, and collectively all of the mobile stations in the communication system, is limited.
In another aspect of the present invention, channel estimation is performed at the network infrastructure of the uplink channel characteristics responsive to the detection at the network infrastructure of the uplink sounding bursts. As a result of the channel estimation, selection is made of values of one or more link parameters to facilitate communication of subsequently-generated communication signals by the mobile station to optimize better the communication quality of transmission of such signals. The coding rate, modulation format, power control step size, retransmission limits, and timer values are all exemplary of link parameters which are selectable responsive to channel estimation during operation of an embodiment of the present invention.
Responsive to the selection, a link parameter signal is generated and transmitted to the mobile station to inform the mobile station of the selected link parameter of which the subsequently-generated communication signal is to exhibit. Thereby, the mobile station is able to transmit communication signals in a manner to optimize communication quality levels.
In one implementation, an embodiment of the present invention is operable in a TDMA (time-division, multiple-access) cellular communication system, such as a GSM (global system for mobile communications) system which provides for GPRS (general packet radio service). As defined in such a system, GPRS messages are transmitted in discrete bursts. For instance, when a GPRS message is to be transmitted by a mobile station operable in the GSM system, a GPRS message is assigned to a channel formed of a frequency and time slot combination. In operation, an embodiment of the present invention determines link parameters of the GPRS message to be transmitted by the mobile station. Selection is made in a manner to facilitate communication of the message at an acceptable quality level. Sounding bursts are periodically generated by the mobile station when the mobile station is in a standby mode.
The sounding bursts are transmitted by the mobile station according to a sounding schedule which is provided to the mobile station by way of a control signal broadcast by the network infrastructure on a broadcast control channel. In the exemplary implementation, the sounding schedule broadcast by the network infrastructure assigns each mobile station to a sounding schedule responsive to the ESN of the mobile station. Thereby, a level of control is exerted upon the mobile stations when the mobile stations generate the sounding bursts on random access channels. The sounding bursts are detected at the base station system of the network infrastructure. Two or more sounding bursts are utilized at the network infrastructure to estimate the channel characteristics of the uplink channel upon which the sounding bursts are transmitted and upon which a GPRS message shall subsequently be transmitted. Responsive to the analysis and channel estimation, a selection is made of one or more link parameters by which the GPRS message is to be transmitted. The coding rate, modulation format, power control step size, retransmission limits, timer values, etc., are all exemplary of parameters selectable responsive to the analysis of the sounding bursts. A signal identifying to the mobile station the selection of the one or more link parameters is transmitted to the mobile station, and a GPRS message subsequently transmitted by the mobile station is generated in a manner complying with the instructions of the link parameter signal provided to the mobile station.
Thereby, a quantitative manner is provided by which to select the link parameter or parameters thereby to improve the quality of communications in the communication system.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a mobile station operable in a radio communication system having network infrastructure and with which the mobile station communicates by way of a radio link. An uplink channel and a downlink channel are defined upon the radio link. The mobile station is operable alternately in a ready state and a non-ready state. When the mobile station is operated in a selected non-ready state, setting of link parameters to improve communication qualities of communications by the mobile station with the network infrastructure is facilitated. A burst signal generator generates and transmits uplink channel sounding bursts to the network infrastructure at selected times when the mobile station is operated in the selected non-ready state. A burst signal controller is coupled to receive indications instructing the mobile station of the selected times at which the burst signal generator generates the uplink channel sounding bursts. The burst signal controller is operable responsive thereto to control when the burst signal generator generates the uplink channel sounding bursts.
Additionally, in these and other aspects, apparatus, and an associated method, is further provided for the network infrastructure of a radio communication system in which a mobile station communicates by way of a radio link upon which an uplink channel and a downlink channel are defined with the network infrastructure. The mobile station is operable alternately in a ready state and a non-ready state. The network infrastructure facilitates setting of link parameters to improve communication qualities of communications by the mobile station with the network infrastructure. A burst signal detector is coupled to receive indications of burst signals generated by the mobile station. The burst signal detector determines values representative of the burst signals. A link parameter selector is coupled to receive indications of the values representative of the burst signals. The link parameter selector selects at least one link parameter to be exhibited by communication signals generated by the mobile station. And, a parameter link signal generator is coupled to the link parameter selector. The parameter link signal generator generates a parameter link signal for transmission upon the downlink to the mobile station to instruct the mobile station to cause communication signals generated thereat to exhibit the at least one link parameter.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.